Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.33   6.549%   $221.9735   $221.97   $221.95   $222.00  
  Purchase #2 $242.28   10.105%   $266.7624   $266.76   $266.75   $266.80  
  Purchase #3 $118.55   3.728%   $122.9695   $122.97   $122.95   $123.00  
  Purchase #4 $46.97   3.347%   $48.5421   $48.54   $48.55   $48.50  
  Purchase #5 $195.61   3.589%   $202.6304   $202.63   $202.65   $202.60  
  Purchase #6 $169.79   9.751%   $186.3462   $186.35   $186.35   $186.30  
  Purchase #7 $192.71   3.354%   $199.1735   $199.17   $199.15   $199.20  
  7 purchase totals = $1,174.24       $1,248.3976   $1,248.39   $1,248.35   $1,248.40